First it is not really a virutal IP address, just an additional IP addresses from what you have described.
Just go into the CFGTCP option 1 Work with TCP/IP Interfaces and add another IP address using the same Ethernet line description you used in the xxx.1.3.87 IP address. You can have multiple IP addresses assigned to the same physical line.
We did this for Lotus Domino machines with each logical Domino server using its’ own IP address but all going throught the same Ethernet line.
For virtual ethernet that would be internal IP addresses talking to one another across LPARs. That is a different set up depending on the class of hardware you have.
Let me know if you have any questions.